1. Field of the Invention
The present invention relates to an apparatus for producing magnetic rollers (MGR) having multiple magnetic poles.
2. Description of Prior Art
Magnetic rollers are essential elements utilized in electro-photographic systems. A magnetic roller is always formed with multiple magnetic poles, either symmetric or asymmetric.
A conventional technique for producing magnetic rollers is to adhere Sr- or Ba-ferrite strips to a steel bar and subsequently machine the ferrite strips into magnetic rollers. This technique has a drawback that the ferrite strips are often slightly misaligned, resulting in mispositioned magnetic poles. In addition, magnetic fields of the magnetic strips are often degaussed after machining.
In another conventional technique, a method similar to that used in magnetizing magnet rings that are employed in motors is utilized to magnetize a magnetic roller having a length longer than 22 cm. The method of producing magnet rings is adapted to magnetize magnet rings with a length less than 3 cm. Therefore, with such a length longer than 22 cm, it is a drawback of this technique that contacts between magnetic heads and the surface of magnetic roller are often not tight enough to produce magnetic poles having uniformly distributed magnetic fields. In addition to this drawback, the magnetic roller is often difficult to be separated from the magnetic heads due to magnetic forces produced after magnetization.
To solve the problem found in magnetizing a magnetic roller having a substantial length, Kodak company of U.S.A. developed a technique which divides a 30-cm magnetic roller into twelve 2.5-cm magnet rings and then combines each magnetized 2.5-cm magnet ring into a 30-cm MGR. It is a drawback of this technique that magnetic leakage is present at the joint of two 2.5-cm magnetic rings, causing unevenly distributed magnetic fields.